This invention relates generally to field emission displays and manufacturing methods, and more particularly to field emission displays having focus grids.
As is known in the art, field emission displays (FEDs) include an array of field emitting cathodes, an array of control, or gate electrodes, and a cathodoluminescent anode. Each one of the control electrodes is associated with a corresponding display pixel and controls the flow of electrons between the cathodes and the corresponding anode pixel. In a monochromatic array, each pixel corresponds to either a so-called xe2x80x9cblackxe2x80x9d or xe2x80x9cwhitexe2x80x9d display luminescence; in a color display each pixel corresponds to a luminous blend of a plurality of, typically three colors.
In order to achieve a relatively bright display, (i.e., up to the order of 10,000 foot lamberts) with typical cathodoluminescent efficiencies, a voltage in the order of 10,000 volts is required between the cathode and anode. In order to reduce the effect of electron beam spreading and its concomitant reduction in picture resolution, cathode to anode separations of less than 3-4 millimeters are required. However, in order to prevent arcing between the anode and cathode with 10,000 volts therebetween, an anode to cathode separation in the order of 3-4 millimeters, or greater, is required. Thus, a compromise must be made between resolution and brightness.
In accordance with the present invention, a field emission display is provided having a plurality of cathodes; a cathodoluminescent anode; a plurality of control electrodes for controlling the flow of electrons between the cathodes and the anode; a focus grid comprising an apertured, conductive sheet; and a dielectric material disposed on the focus grid between the conductive sheet and the control electrodes.
With such an arrangement, the dielectric material prevents the focus grid from electrically contacting the control electrodes.
In accordance with another feature of the invention, a field emission device is provided comprising a cathode having an array of pixels. Each pixel has a plurality of field emitters and corresponding gate electrodes to emit electrons. An anode is distally disposed with respect to the cathode. A focus grid is disposed between the anode and the cathode. The focus grid has an array of apertures. Each aperture is disposed coaxial with a corresponding pixel of the cathode to focus electrons from the plurality of field emitters of the pixel of the cathode toward the anode. A dielectric material is disposed on a surface of the focus grid facing the gate electrodes to prevent electrical contact between the surface of the focus grid and the gate electrodes. Further, it has been discovered that high angle electrons emitted by each pixel are inhibited from passing through the focus grid aperture associated with an adjacent pixel to eliminate cross-talk. It is believed that surface charge forms on the dielectric material and acts as an additional focusing structure that reduces the number of high angle electrons emitted from one pixel that pass through an adjacent focus grid aperture and impinge upon the anode far from the desired location.
In accordance with another feature of the invention, a field emission device is provided comprising a cathode having an array of pixels. Each pixel has a plurality of field emitters and corresponding gate electrodes formed as a cathode structure to emit electrons. An anode is distally disposed with respect to the cathode. A focus grid is disposed between the anode and the cathode. The focus grid has an array of apertures. Each aperture is disposed coaxial with a corresponding pixel of the cathode to focus electrons from the plurality of field emitters of the pixel of the cathode toward the anode. A dielectric layer is disposed between, and in contact with, the focus grid and the cathode structure to provide an integral structure which prevents contact between the surface of the focus grid and the gate electrodes. Further, the dielectric layer prevents high angle electrons emitted by each pixel from passing to the anode as electrons emitted from an adjacent pixel. Still further, the focus grid and the array of pixels are a unitary structure so that the focus and cathode structure cannot move relative to each other.
In accordance with another feature of the invention, a method is provided for forming a grid for a field emission display. The method includes the step of spraying a dielectric material towards a surface of the grid while a vacuum draws the spray from the surface through apertures in the grid.